### Video Transcript

The diagram shows a sketch of 𝑦 is
equal to cos of 𝑥 degrees for negative 180 is less than or equal to 𝑥 which is
less than or equal to 540. Part a) Write down the coordinates
of 𝐴.

Remember the graph of 𝑦 is equal
to cos of 𝑥 is periodic. That means it repeats and it has a
period. It repeats every 360 degrees. This is a useful place to
start.

We know that the cos graph
intersects the 𝑦-axis at one. It gets back to one at 360
degrees. So 360 degrees must be the point on
the 𝑥-axis at which the graph reaches one again.

We can halve this. And we now know that the graph
reaches negative one at 180. Halving again, it intersects the
𝑥-axis at 90 and then 270. We add 90 to 360. And we can see that it intersects
the 𝑥-axis once again at 450 degrees. And the graph is also symmetrical
in the 𝑦-axis. So we can add negative 90 and
negative 180.

Once we have all of that
information written down, we can simply read the coordinates for 𝐴 straight from
the graph. 𝐴 has coordinates 180, negative
one.

b) Write down the coordinates of
𝐵.

We can see that 𝐵 is the point
where the graph intersects the 𝑥-axis for the third time. The coordinates of 𝐵 are 450,
zero.

The values on the 𝑥-axis represent
an angle there in degrees. So we can say that the coordinates
of 𝐴 are 180 degrees, negative one and the coordinates of 𝐵 are 450 degrees,
zero.